Digital projectors, such as digital mirror devices (DMD) and liquid crystal display (LCD) projectors, cast high quality images onto a viewing surface. Both DMD and LCD projectors utilize high intensity burners and reflectors to generate the light needed for projection. Light generated by the burner is concentrated as a ‘fireball’ that is located at a focal point of a reflector. Light produced by the fireball is directed into a projection assembly that produces images and utilizes the generated light to form the image. The image is then projected onto a viewing surface.
Efforts have been directed at making projectors more compact while making the image of higher and higher quality. As a result, the lamps utilized have become more compact and of higher intensity. An example of one type of such lamps is knows as a xenon lamp. Xenon lamps provide a relatively constant spectral output with significantly more output than other types of lamps without using substantial amounts of environmentally harmful materials, such as mercury. In addition, xenon lamps have the ability to hot strike and subsequently turn on at near full power.
Higher intensity lamps produce high, even extreme heat. If this heat is allowed to accumulate in the lamp, it may shorten the useful life of the lamp. For example, a xenon lamp operating on 330 watts (W) of input power often produces about 69 W of visible light. The remaining power generates infrared radiation, black body radiation, and ultraviolet radiation or is consumed by electrical losses. As a result, the light generation assembly needs to dissipate about 250 W of power. Some designs attempt to dissipate the energy by reflecting the radiation away from the lamp and removing the heat with isolated heat sinks.
In addition, the ceramics used for reflector bodies typically have low thermal coefficients. As a result, ceramic reflector bodies do not absorb much heat. Instead, the heat is dissipated by separate heat sinks. These heat sinks are frequently coupled to the reflector by the anode, which provides a path of low thermal resistance. As a result of the low heat transfer rate of the ceramic, the amount of heat dissipated by the heat sink depends on the size and thermal resistance of the anode.